Re: [PATCH] treewide: remove current_text_addr

[Peter Zijlstra <peterz@infradead.org>]

On Sun, Aug 26, 2018 at 07:52:59PM -0700, Nick Desaulniers wrote:
> On Sun, Aug 26, 2018 at 1:25 PM Linus Torvalds

> > Instead, maybe we could encourage something like
> >
> >   struct kernel_loc { const char *file; const char *fn; int line; };
> >
> >   #define __GEN_LOC__(n) \
> >         ({ static const struct kernel_loc n = { \
> >                 __FILE__, __FUNCTION__, __LINE__  \
> >            }; &n; })
> >
> >   #define _THIS_LOC_ __GEN_LOC__(__UNIQUE_ID(loc))
> >
> > which is a hell of a lot nicer to use, and actually allows gcc to
> > optimize things (try it: if you pass a _THIS_LOC_ off to an inline
> > function, and that inline function uses the name and line number, gcc
> > will pick them up directly, without the extra structure dereference.
> >
> > Wouldn't it be much nicer to pass these kinds of "location pointer"
> > around, rather than the nasty _THIS_IP_ thing?
> >
> > Certainly lockdep looks like it could easily take that "const struct
> > kernel_loc *" instead of "unsigned long ip". Makes it easy to print
> > out the lockdep info.

> This is extremely reasonable.  I can follow up with the lockdep folks
> to see if they really need _THIS_IP_ to solve their problem, or if
> there's a simpler solution that can solve their needs.  Sometimes
> taking a step back and asking for clarity around the big picture
> allows simpler solutions to shake out.

What problem are we trying to solve? _THIS_IP_ and _RET_IP_ work fine.
We're 'good' at dealing with text addresses, we use them for call stacks
and all sorts. Why does this need changing?